One of the key problems of nuclear reactor plants with liquid-metal coolants is corrosion of reactor structural materials. To prevent corrosion, the technique for formation of protective oxide coatings is used. The corrosion resistance of reactor structural materials, for example, steel, depends on the integrity of these coatings.
It should be noted that the mentioned problem may occur both in nuclear reactor plants with non-liquid-metal coolants and in non-nuclear reactor plants. Although, this invention is described in relation to nuclear reactor plants with liquid-metal coolants, it also can be used both in nuclear reactor plants with non-liquid-metal coolants and in non-nuclear reactor plants.
Oxygen can be applied for the purpose of formation of oxide coatings. Patent RU2246561 (issued on Feb. 20, 2005) discloses the method for increasing the oxygen concentration in the coolant by way of injecting the oxygen gas directly into the coolant, or supplying oxygen to the coolant surface, for example, into the gas chamber close to the coolant—in the latter case oxygen penetrates the coolant by way of infusion. Due to the fact that iron, chrome, and other components of structural materials have higher chemical affinity for oxygen, than coolant components, such as lead and/or bismuth, oxygen, inserted into the liquid metal coolant in the form of oxides of the coolant components, will oxidize components of structural materials and, at adequate oxygen concentration, will form protective oxide coatings on the surface of reactor walls. To ensure this kind of effect, oxygen concentration in the coolant is to be maintained within specified limits which depend on the reactor design and structural materials, as well as on the type and composition of coolant.
Besides oxygen the other gases may be injected into the coolant. One of the disadvantages of such method is that gas injection into the coolant results in formation of bubbles floating to the coolant surface and gas from these bubbles enters the above-coolant space. While being in the coolant the dust, solidphase particles and components dissolved in the coolant may penetrate the gas bubbles. Therefore, gas injected into the coolant becomes contaminated by dust, solidphase particles and components after staying in the coolant and entering above-coolant space. Reuse of such gas, in particular, its reinjection into the coolant, results in contamination of the coolant and reactor equipment and, therefore, causes equipment faults and reduction of operating life of the equipment and reactor as a whole.